Electrochemical capacitors are a class of high-rate energy storage/discharge devices which use electrolytes and electrodes of various kinds. Electrochemical capacitors, like batteries, are essentially energy storage devices. However, unlike batteries, they rely on charge accumulation at the electrode/electrolyte interface to store energy. Charge storage in electrochemical capacitors therefore is a surface phenomenon. Conversely, charge storage in batteries is a bulk phenomenon occurring within the bulk of the electrode material. As a result of the differences in the charge/discharge mechanism between capacitors and batteries, the discharge profiles and discharge rates of the two devices are radically different.
Electrochemical capacitors can generally be divided into one of two subcategories. Double layer capacitors in which the interfacial capacitance at the electrode/electrolyte interface can be modeled as two parallel sheets of charge; and redox reaction based capacitor devices in which charge transfer between the electrolyte and the electrode occurs over a potential range, and is the result of primary, secondary, tertiary or higher oxidation/reduction reactions between the electrode and the electrolyte. These types of electrochemical capacitors are currently being developed for high pulse power applications.
Heretofore, electrochemical capacitor devices have suffered from problems associated with the manufacture and packaging of such devices. It is the nature of electrochemical capacitors to require relatively small packages which develop high pulse power spikes. Prior art methods of assembling such devices however substantially increased the thickness of the device, as well as the complexity of the manufacturing process. Increased complexity resulted in manufacturing defects which caused yield losses. Moreover as the package became thicker due to processing, the introduction of electrode equivalence series resistance (ESR) reduced the efficiencies of the devices fabricated.
Accordingly, there exists a need to provide a new process for manufacturing and assembling electrochemical capacitor devices. This process should emphasize ease and convenience of manufacturing while providing as thin a profile device as possible so as to reduce ESR and optimize gravimetric and volumetric energy and power densities. These devices should also be fabricated with electrolytes better tailored to the needs of electrochemical capacitors.